1. Field of the Invention
This invention relates to lens mountings having incorporated therein a motor by which movement of a movable lens system is controlled.
2. Description of the Prior Art
There have been known many techniques of employing the reactive force of electromagnetic induction for moving some members or units within the lens mounting. As examples of prior art relating to the technique of controlling the operation of a diaphragm unit in the lens mounting by an electromagnetic induction mechanism, mention may be made of U.S. Pat. Nos. 3,687,042 and 4,113,359.
Further, in relation to a motorized focusing technique it has been the common practice in the art of motion picture cameras to incorporate a small-sized D.C. motor in the lens mounting with the driving torque of said motor being transmitted through a gear train to the holder for the focusing lens. The use of such a motor driven focusing mechanism produces a problem in that as the motor is positioned on a lens barrel, for example, in a space between the body tube and the casing of the lens mounting, the outer appearance becomes awkward with a large outward projection only at that portion which contains the motor. Up to now, the portion comprising the lens barrel has been perfectly round over its entire length. Thus such an awkward appearance cause in users a feeling of discomfort. This is not only undesirable from the standpoint of industrial design but also because it involves an objectionably large increase in the complexity of the structure of the lens mounting mechanism.
Another prior art proposal involves the use of a linear motor in controlling the movement of the focusing lens as disclosed in U.S. patent application Ser. No. 396,030 filed July 7, 1982 (corresponding to Japanese Laid-Open Patent Application No. Sho 58-10706 published Jan. 21, 1983). In this case, however, the stator of the motor must be as elongated axially as much as the range of movement of the focusing lens, and the rigorous requirement for the control of adjustment in position of the focusing lens is also difficult to fulfill.
Another type of lens focus adjusting mechanism using an epicyclic motor is known in U.S. Pat. No. 4,152,060. This motor is constructed with a stator concentric to the optical axis of the focusing lens and a tubular armature arranged in eccentric relation to the optical axis upon energization to rotate epicyclically relative to the stator. A lens holder for the focusing lens has a central axis substantially coincident with the optical axis and is rotatably mounted in the interior of the armature through an intermediary of which the center of rotation is in coincidence with the optical axis and of which rotative motion causes axial movement of the lens holder. The mechanism further includes a drive connection for transmitting epicyclic motion of the armature to rotative motion of the lens holder. From this description it seems that the structure of a lens mounting adapted for use of such focusing mechanism will be very complicated and therefore the assembling and adjusting operations will be very difficult to carry out.
Since it is conventional for a lens mechanism to be called lens is round in crossection, the parts of the lens mounting are designed on the basis of this form, and constituent parts such as the lens holder, fixed body, focusing actuator, zoom actuator, helicoid member and cam member are necessarily of a round shape. Therefore it has been sought to construct the motor usable with the operating mechanism for the focusing lens or zoom lens from only such tubular constituent parts as are compatible with the parts constituting the lens mounting with the advantage that the outer appearance will not have an awkward projection, and the use of the motor will not call for an unduly large increase in the complexity of the structure of the lens mounting mechanism. A device seeking to achieve this object is disclosed in Japanese Laid-Open Patent Application No. Sho 57-186738 published Nov. 17, 1982. This prior art device concerns a lens mounting provided with a space near a holder containing a lens group to be axially moved, wherein a motor is positioned in this space and is fixedly secured to the lens holder. When the motor is energized, the lens holder is driven along with this motor to move axially to effect focusing or zooming. A practical example of this motor is shown in an annular form.
It is also known to provide a stepping motor incorporated in a lens mounting wherein the movable lens is driven to move by the stepping motor as disclosed in Japanese Laid-Open Patent Application No. Sho 56-147132. This stepping motor is of the variable reluctance (VR) type and is arranged between the lens holder and the lens case. Rotative movement of the motor is converted to axial movement of the lens holder by a drive connection.